We demonstrate efficient and compact 1xN wavelength-demultiplexing by using objective-first inverse design algorithm. Ultra-high device performances were achieved for the certain designs of 1x2, 1x3, and 1x4 demultiplexers with very small footprints at the orders of a few microns. The presented 1x2, 1x3, and 1x4 devices operate at the wavelength sets of 1.31μm, 1.55 μm; 1.31 μm, 1.47 μm, 1.55 μm, and; 1.31 μm, 1.39 μm, 1.47 μm, 1.55 μm, respectively. The transmission efficiencies at the corresponding target wavelengths of each vertically or horizontally aligned channels were obtained mostly to be near-unity together with very small crosstalk ranges of around 0.01% - 1.2%. The inverse design approach allowing the implementation of more than four output channels together with the novel functionalities will pave the way for compact and manufacturable 1xN couplers, which is of ultimate significance for integrated photonics.
We propose and demonstrate compact on-chip optical filters with ultra-high efficiencies, which are designed via the recently-emerged objective-first inverse design algorithm. The all-dielectric high-pass, low-pass and all-pass filters presented in this study operate within the telecommunication wavelength spectrum of 1260 - 1625 nm. The high-pass filter shows an outstanding performance for the transmission efficiency higher than the frequency of 210 THz and an effective suppression of the other spectral region. Also, the proposed low-pass filter exhibits high transmission and significant blocking at the ranges of 170 Thz-205 Thz and 205 Thz-240 Thz, respectively. Furthermore, the designed allpass filter possesses notable spectral transmissivity and blocking characteristics. The promising features of the structures were also verified via the finite-difference time-domain method. Such manufacturable optical filters with great device performances are favorable candidates for next-generation photonic applications.
We propose octagonal quasi-crystal designs providing effective light confinement for different resonance frequencies through the structural modification with the utilization of low-symmetric photonic unit cells. The effect of rotational symmetry reduction on the cavity resonance appearing in the corresponding photonic bandgap of each structure has been investigated. Relatively small dielectric cylinders have been additionally located at discrete angular positions with particular distances from the center of the each core cylinder and the noteworthy resonance peaks have been observed to emerge in the bandgaps. Rotational symmetry of the proposed structures is to be modified by varying the angular displacement of the smaller quasi-crystalline rods with the angle θ in terms of the x-axis of the small rod. The successful demonstration of tunable resonance modes has been achieved numerically and experimentally for the first time by tailoring the positional parameters and reducing the crystalline symmetry. Strongly localized modes in the proposed quasi-crystals have great potential for various slow light applications along with other technologies such as sensors, lasers and memory units.
We propose and demonstrate photonic crystals (PCs) providing backward-directional propagation of surface slow waves, which is significant for potential PC-based photonic applications. An effective pathway for backward directing of surface slow light along with the modification of other important characteristics is presented via implementing surface morphological diversity in PCs. With the surface orientation angle varying from 900 to 300, the newly appearing bands inside the band gap shift to higher frequencies, and negative group indices up to -100 are observed as the strong indication of backward propagation. Furthermore, dependence of the propagation direction on the surface corrugation angle has been verified via detailed time-domain analyses and microwave experiments using dipole source. As obtained from both the numerical and experimental results, for instance, the structure with 600 provides a well-defined backward propagation. In addition, normalized-delay-bandwidth-product can easily be modified by varying the surface orientation angle in the proposed structures according to the necessities of the application. Furthermore, the group velocity dispersion spectra extracted for each periodic structure exhibit considerably high-range near-zero values as 0.139 ps<sup>2</sup>/m at 900 for the range of 495.54-501.25 nm and 0.176 ps<sup>2</sup>/m at 85° for the range of 495.66-501.25 nm. Third order dispersion spectra also obtained for the proposed PCs show near-zero values as 0.098 ps<sup>3</sup>/m at 900 and 0.113 ps<sup>3</sup>/m at 85° in the corresponding frequency regimes. Facile control of the key characteristics such as backward-directed surface wave propagation in the periodic dielectric structures having morphological diversity serves a great potential for nextgeneration photonic applications.